﻿using System;
using System.Linq;
using Xamarin.Forms;

namespace Xfx.Controls.Droid.Forms.Internals
{
    [Android.Runtime.Preserve (AllMembers = true)]
    internal class PinchGestureHandler
    {
        double _pinchStartingScale = 1;

        public PinchGestureHandler(Func<View> getView)
        {
            GetView = getView;
        }

        Func<View> GetView { get; }

        // A View can have at most one pinch gesture, so we just need to look for one (or none)
        PinchGestureRecognizer PinchGesture => GetView()?.GestureRecognizers.OfType<PinchGestureRecognizer>()
            .FirstOrDefault();

        public bool OnPinch(float scale, Point scalePoint)
        {
            View view = GetView();

            if (view == null)
                return false;

            PinchGestureRecognizer pinchGesture = PinchGesture;
            if (pinchGesture == null)
                return true;

            var scalePointTransformed = new Point(scalePoint.X / view.Width, scalePoint.Y / view.Height);
            pinchGesture.SendPinch(view, 1 + (scale - 1) * _pinchStartingScale, scalePointTransformed);

            return true;
        }

        public void OnPinchEnded()
        {
            View view = GetView();

            if (view == null)
                return;

            PinchGestureRecognizer pinchGesture = PinchGesture;
            pinchGesture?.SendPinchEnded(view);
        }

        public bool OnPinchStarted(Point scalePoint)
        {
            View view = GetView();

            if (view == null)
                return false;

            PinchGestureRecognizer pinchGesture = PinchGesture;
            if (pinchGesture == null)
                return false;

            _pinchStartingScale = view.Scale;

            var scalePointTransformed = new Point(scalePoint.X / view.Width, scalePoint.Y / view.Height);

            pinchGesture.SendPinchStarted(view, scalePointTransformed);
            return true;
        }
    }
}